The present invention relates to an electron beam tube of the type having a gettering surface and an electrically heatable cathode whose heating power is less than 250 mW, and in particular less than 100 mW.
Electron beam tubes of this type are known in the art. It is also known to improve the vacuum in such a tube by vaporizing a getter, preferably of barium, so that a thin getter film is produced on the interior surfaces of the tube. These getter surfaces are able to bind residual gases in the tube.
It has now been found that, particularly in tubes having an extremely low cathode heating power, the danger of the cathode being poisoned by residual gases is particularly high. These residual gases generally contain hydrocarbons, such as, for example CH.sub.4 or C.sub.2 H.sub.6, which are absorbed only insufficiently or not at all by the getter materials, particularly by barium.